Cellular and molecular mechanisms of fatty infiltration in paraspinal muscles in spine-specific sarcopenia

Spine-specific sarcopenia has recently been recognized as a localized degenerative disorder distinct from systemic sarcopenia. Its main symptom is selective degeneration of paraspinal muscles and is closely associated with various spinal disorders and postoperative prognosis. One of the core features of this condition is fatty infiltration (FI), which more accurately reflects muscle quality and functional impairment than muscle cross-sectional area (CSA). FI is closely associated with paraspinal muscle atrophy and is regulated by multiple interrelated mechanisms, including pathological activation of fibro-adipogenic progenitors (FAP), denervation-induced loss of trophic support, biomechanical alterations, and abnormal adipokine signaling pathways. At present, diagnostic indicators used for systemic sarcopenia show limited validity in the assessment of paraspinal muscles, highlighting the urgent need to establish an evaluation framework for spine-specific sarcopenia. By reviewing the major mechanisms underlying fatty infiltration of the paraspinal muscles and summarizing recent advances in imaging assessment of spine-specific sarcopenia, this article provides a basis for improving comprehensive evaluation of paraspinal muscle degeneration in both clinical and research settings.